In Drosophila, chromosome ends are maintained by the targeted transposition of two retrotransposons, HeT-A and TART. In the wild type, the frequency of transposition is sufficient to balance the gradual chromosome shortening due to incomplete DNA replication, although mutations that increase or decrease this frequency have been described. A transgene inserted into the telomere between the subterminal telomere associated sequence (TAS) and the terminal HeT-A/TART array is repressed and variegates. This variegation, termed telomeric position effect (TPE), appears to be due to an interaction of repression induced by TAS and activation initiated by HeT-A. Previous studies have identified genetic conditions in which TPE occurs and conditions in which it is suppressed. The purpose of this project is to identify changes in chromatin structure associated active and suppressed TPE. Preliminary studies using chromatin immunoprecipitation indicate a strong signal for methylated histone H3 at lysine 79 at both TAS and HeT-A when TPE is active. The suppressed condition has not yet been tested, but it is known that mutations that disrupt the enzyme that catalyses this histone modification suppress TPE.